Method and device for the adaptive regulation of power

ABSTRACT

A method and a device for adaptively controlling power in a radar device having a radar transmitter and a radar receiver are provided, in particular for applications in vehicles. The radar signals are emitted, and radar signals reflected off of target objects are received and checked for irregularities. The transmitting power of the radar transmitter is reduced when irregularities occur which are attributable to interference caused by neighboring radar transmitters.

FIELD OF THE INVENTION

The present invention is directed to a method and a device foradaptively controlling power of transmitted signals of a radar detector.

BACKGROUND INFORMATION

In the automotive sector, systems which measure the distances andvelocities of objects around one's own vehicle by using microwaves andapplying the radar principle are in use. These objects can be vehicleswhich are actively taking part in the highway traffic or some sort ofobstacles on or near the road. Keyless remote-entry systems for vehicles(keyless entry/comfort entry/keyless go systems) also make use of thesetechnologies. In the known systems, high-frequency energy is radiated ina frequency range in the gigahertz range, at a mid-frequency of 24,125GHz and with a two-way bandwidth of several GHz. Typical antennas have adirectional characteristic (i.e., an antenna radiation pattern) of 80degrees*20 degrees. In practice, the transmission range is about 20 m.The risk inherent in such systems is that unacceptably high signallevels occur, even in frequency ranges that have been blocked in favorof other services, e.g., frequency ranges that are reserved for radioastronomy or also for radio relay services. Unacceptably high signallevels can occur, for example, when a substantial number of theabove-mentioned systems in the surrounding, for example several hundred,are simultaneously put into operation. This can be the case, forexample, when a large number of vehicles are moving on multilane urbanstreets. Similar problems arise in large parking lots at sportsfacilities or shopping centers when, for example, after a big eventends, hundreds of vehicles start moving at the same time and leave theparking lot. For the most part, these problems only occur when thevehicles are at standstill or traveling at a relatively slow speed. Thisis because, at higher speeds, the distances between the vehiclesincrease again, and the vehicle density decreases correspondingly.Furthermore, the spatial proximity of many sensors also causes heavymutual interference, which, when working with adaptive sensors,increasingly leads to additional measurements being taken, although someobjects may have actually already been reliably detected.

Published German Patent Application DE 100 65 521 describes a method anda device for detecting moving or stationary objects using radarradiation, in particular for use in motor vehicles, where, in order todetect objects, pulse-modulated carrier waves are radiated, whosereflected portions are then received and evaluated. In this context, bytransmitting an unmodulated carrier in the time intervals between twoadjacent pulses, a Doppler measurement can additionally be performed,thereby enabling a reliable velocity measurement to be taken.

When irregularities are detected in received signals, the transmittingbranch of the radar may be switched off. Thus, no more transmissionsignals are emitted by the transmitting antenna. However, correlationpulses from a pulse transmitter continue to be transmitted to thereceiving branch of the radar sensor. If it turns out in the processthat object information is still received, then an illusory object mustbe inferred.

SUMMARY

The present invention minimizes signal irregularities in radar detectorsby using an adaptive power control. As soon as it becomes apparent thatthe interference is unacceptably high due to a heavy traffic density, anappropriate power adaptation is carried out. Once objects have beenreliably detected, the measurement repetition rate may be reduced. Inaddition, the possible detection range does not need to be utilized upto the maximum value; instead, it may be stopped once a limit to beregarded as useful is reached, such as of two to five detected objects,especially as the power requirement increases with the fourth power ofthe distance. Provided that a ground speed is measurable, at a low speedof less than about 20 to 40 km/h or at standstill, and in the case offar away objects, the power may likewise be reduced by limiting theaverage power, the measurement repetition frequency, or the maximumdistance. The relatively low speed makes it unlikely that objects wouldappear unexpectedly. If necessary, however, a measurement may also bemade in-between, up to the maximum range, in order to secure theintervening space up to the furthest object, and thereby enhance thesafety on the whole. The speed information may be obtained from thewheel speeds, from a radar measurement which records the ground speed,or from an SRR (secondary surveillance radar) measurement by estimatingstationary objects. While the first two mentioned methods lead to veryreliable results, the last-mentioned method additionally requires anexact classification into illusory objects, on the one hand, andtangible moving objects, on the other hand, to attain reliable results.Since in situations of high traffic density and, thus, a highconcentration of sensors, the interfering influences increase, in whichcase the present invention also makes it possible to adaptively reducethe power within a relatively short range, provided that reliablydetected objects exist. The present invention makes it possible for thetransmitting power to be reduced, thereby facilitating an approval inconformance with UWB (ultra-wide band) criteria. By reducing thetransmitting power, the interference immunity may be further enhanced.This means that there is less mutual interference among adjacentvehicles. The reduced transmitting power leads to a lower currentconsumption, which is beneficial in terms of energy usage. Also, becauseof the reduction in load, one can expect a longer service life. Byapplying the approach of the present invention, assuming a maximumdistance of 20 m and a breaking off of the emissions in the distancestages 5 m, 10 m or 15 m, the average power could be reduced by 30 db,15 db, and 6 dB, respectively. Consequently, the spectral density is, ofcourse, also lowered. In addition, the transmitted power could also belowered by approximately 6 to 20 dB.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a conventional radar device of the related art;

FIG. 2 shows a motor vehicle having radar devices.

FIG. 3 shows a graph of a radar signal of a radar device.

FIG. 4 shows a graph of radar signals having interference of varyingintensity.

FIG. 5 shows a block diagram of a radar device.

FIG. 6 shows a first flow chart illustrating the reduction of power.

FIG. 7 shows a second flow chart illustrating the reduction of power.

DETAILED DESCRIPTION

In a block diagram, FIG. 1 shows a radar device having a correlationreceiver as known in the art. A pulse generator 2 induces a transmittingdevice 1 to emit a transmitted signal 6 via an antenna 4. Transmittedsignal 6 impinges on a target object 8, where it is at least partiallyreflected, and returns to receiver 14. Received signal 10 is received byantenna 12. In this context, antenna 12 and antenna 4 may be identicaland be switched between transmitting and receiving operation. Uponreceipt of received signal 10 by antenna 12, received signal 10 isrouted to receiver 14 and subsequently fed via a filter device havingA/D conversion 16 to an evaluation device 18. An exceptional feature ofsuch a radar device, which has a correlation receiver, is that receiver14 receives a reference signal 20 from pulse generator 2. Receivedsignals 10 received by receiver 14 are mixed in receiver 14 withreference signal 20. The correlation operation makes it possible toinfer the distance of a target object, for example, on the basis of thetemporal delay from emission of a radar signal until receipt of a radarsignal reflected off of a target object.

It is possible to operate a plurality of substantially identical, e.g.,between 4 and 16, radar sensors on one vehicle. This is clearly shown inFIG. 2, which illustrates a motor vehicle 20 having a multiplicity ofradar sensors 21. Radar sensors 21 are interconnected via a bus to oneanother and to control devices. For example, a device 24 for providing apark distance control and for detecting a blind spot, a device 26 forthe precrash function, as well as a device 28 for facilitating travel instop-and-go traffic are provided.

FIG. 3 shows a typical radar signal which is transmitted by a radardevice working in the short range. When working with a radar device ofthis kind, high-frequency energy is radiated in a frequency range in thegigahertz range, at a mid-frequency of 24,125 GHz and with a two-waybandwidth of several GHz.

FIG. 4 shows typical received signals which have been picked up by aradar device working in the short range. The characteristic curve offirst received signal ES1 shown in the upper part of the diagram issubstantially undisturbed. The characteristic curve of second receivedsignal ES2 shown in the middle area of the diagram is influenced by astrong interference, which may be caused by an FMCW (frequency modulatedcontinuous wave) radar. Third received signal ES3 illustrated in thelower part of the diagram is affected by a very strong interference ofthe same type.

FIG. 5 shows a block diagram of a radar device 520 which is provided formonitoring the immediately adjacent zone around a motor vehicle. Acontrol device 522 supplies energy to radar device 520. Thus, forexample, control device 522 supplies an input voltage of 8 V for radardevice 520. This input voltage is fed to a DC/DC converter 524 whichmakes available a supply voltage of, for example, 5 V for the componentsof radar device 520. Radar device 520 also includes a local oscillator526 which produces a carrier frequency of 24 GHz, for example. Thislocal oscillator is supplied with a bias voltage generated by aconverter 530, which is driven by pulses produced by a clock-pulsegenerator 528. The pulses produced by clock-pulse generator 528, whichmay have a frequency of a few MHz, e.g., 5 MHz, are used to modulate thecarrier signal supplied by local oscillator 526. This modulation iscarried out in the transmitting branch of radar device 520 by aswitching element 532 which is controlled by a pulse shaper 546. Pulseshaper 546, in turn, is likewise driven by the clock frequency ofclock-pulse generator 528. The pulsed signals generated in this mannerare radiated by an antenna 534. In the case that the signals emitted byantenna 534 are reflected off of a target object, for example, thereflected signals are received by an antenna 536. Once the receivedsignals are amplified in an amplifier 538, the signals are fed to twomixers 540 and 542. First mixer 540 then emits a so-called I-signal,while second mixer 542 outputs a 90° out-of-phase Q-signal. In mixers540, 542, the received signals are mixed with the pulsed signals oflocal oscillator 526, this pulsing taking place via a switch 544. Switch544 is driven by a pulse generator 548 which outputs delayed pulses. Forexample, pulses output by pulse generator 548 are delayed by a timeperiod Δt with respect to the pulses from pulse generator 546. Thisdelay is effected by a delay circuit 500. The duration of the delay ofdelay circuit 500 is influenced via a microcontroller 552, whichpreferably includes a digital signal processor. This is accomplished viaa first analog output 554 of microcontroller 552. Via a second analogoutput 560, the I- or Q-signals processed by an amplifier 556 areinfluenced by another, e.g., variable amplification in amplifier 558.This amplifier 558 is controlled by a second analog output 560 ofmicrocontroller 552. The output signal from amplifier 558 is fed to ananalog input 562 of microcontroller 552. Microcontroller 552communicates via an input/output bus 564 with control device 522. Radardevice 520 also includes a so-called notch filter 566, which is suitedfor suppressing monochromatic or nearly monochromatic interferencesignals. Also provided are a PLL (phase-locked loop) circuit 568 and afurther mixer 570. The frequency of an interference signal may beadvantageously determined by tuning PLL circuit 568.

Using the above-described device, it is possible to ascertaininterference in the received signal and to classify the type ofinterference. At this point, as soon as it is determined that thedetected interference is attributable to a high traffic density, anappropriate power adaptation, which may contribute to a reduction in theinterference, is carried out in accordance with the present invention.Once objects have been reliably detected, the measurement repetitionrate may also be reduced. Since fewer radar signals are emitted as aresult, the probability of interference being caused is also reduced. Inaddition, it is not necessary to utilize the maximum possible detectionrange; instead, the detection range may be stopped once a limit to beregarded as useful is reached, e.g., two to five detected objects,especially as the power requirement increases with the fourth power ofthe distance. This is explained below with reference to the flow chartof FIG. 6.

In a first step 60, radar device 520 is operated in normal operation. Inthis normal operation, measurements are taken at regular intervals up toa maximum range of about 20 m. In a step 61; it is checked whetherobjects have been detected within a relatively short range. If this isnot the case, alternative path 61 a is selected, and the normaloperation is continued in accordance with step 60. If, on the otherhand, objects are detected within the relatively short range,alternative path 61 b is selected, and power is reduced in accordancewith step 62 in that measurements are still only taken up to a limitingdistance of n m, where n<20 m. By applying the approach of the presentinvention, assuming a maximum distance of 20 m and limiting theemissions at the distance stages 5 m, 10 m or 15 m, the average powercould be reduced by 30 db, 15 db, and 6 dB, respectively. Consequently,the spectral density is, of course, also lowered. In addition, thetransmitted power could also be lowered by approximately 6 to 20 dB.

An alternative approach for reducing power is explained with referenceto the flow chart shown in FIG. 7. In a first step 70, radar device 520is operated in normal operation. In this normal operation, measurementsare taken at regular intervals up to a maximum range of about 20 m. In asubsequent step 71, it is checked whether the vehicle is stationary orwhether it is moving at a relatively low speed. If this is not the case,alternative path 71 b is selected, and the normal operation is continuedin accordance with step 70. If, however, only a low speed of less thanabout 20 to 40 km/h is measured, or it is determined that the vehicle isstationary, alternative path 71 a may be taken to arrive at step 72. Inthis step 72, it is checked whether objects have been detected in adistance shorter than 20 m. If this is the case, alternative path 72 ais selected, and power is reduced in accordance with step 73 in thatmeasurements are still only taken up to a limiting distance of n m,where n<20 m. The relatively low speed makes it unlikely that objectswould appear unexpectedly. If necessary, however, a measurement may alsobe made in-between, up to the maximum range, in order to secure theintervening space and thereby enhance the safety on the whole. If thisis not the case, alternative path 72 b is selected, and the normaloperation is continued in accordance with step 70.

The speed information may be obtained from the wheel speeds, from aradar measurement which records the ground speed, or from an SRR(secondary surveillance radar) measurement by estimating stationaryobjects. While the first two mentioned methods lead to very reliableresults, the last-mentioned method additionally requires an exactclassification into illusory objects, on the one hand, and tangiblemoving objects, on the other hand, to attain reliable results. Since insituations of high traffic density and, thus, a high concentration ofsensors, the interfering influences increase, the present invention alsomakes it possible to adaptively reduce the power within a relativelyshort range, provided that reliably detected objects exist. The presentinvention makes it possible for the transmitting power to be reduced,thereby facilitating an approval in conformance with UWB (ultra-wideband) criteria. By reducing the transmitting power, the interferenceimmunity may be further enhanced. This means that there is less mutualinterference among adjacent vehicles. The reduced transmitting powerleads to a lower current consumption, which is beneficial in terms ofenergy usage. A longer service life may be expected as well, due to thereduction in load.

1-9. (canceled)
 10. A method for adaptively controlling the power ofsignals transmitted by a radar device having a radar transmitter and aradar receiver, the radar device being mounted in a vehicle, the methodcomprising: transmitting radar signals from the radar transmitter;receiving at the radar receiver radar signals reflected from targetobjects; analyzing the received radar signals reflected from targetobjects for irregularities; and reducing the power of radar signalstransmitted by the radar transmitter if irregularities that areattributable to interference caused by neighboring radar transmittersare detected in the received radar signals reflected from targetobjects.
 11. The method as recited in claim 10, wherein radar signalsare transmitted repeatedly from the radar transmitter, and wherein arepetition rate of transmitting radar signals is reduced ifirregularities that are attributable to interference caused byneighboring radar transmitters are detected in the received radarsignals.
 12. The method as recited in either claim 11, wherein, when thevehicle is one of at a standstill and traveling at a low speed, thepower of radar signals transmitted by the radar transmitter is reducedin comparison to normal transmitting power, whereby a correspondingradar detection range of the radar device is reduced.
 13. The method asrecited in claim 12, wherein the power of radar signals transmitted bythe radar transmitter is reduced in stages, whereby, starting from amaximum power level, the power of radar signals is decreased to a nextlower power level when no target object has been detected in animmediately previous measuring cycle.
 14. The method as recited in claim13, wherein, after the power of radar signals transmitted has beendecreased to the next lower power level, the power of radar signalstransmitted is briefly increased in periodic intervals to a higher powerlevel, in order to increase the probability of detecting target objectsat increased distances.
 15. The method as recited in claim 13, wherein,after the power of radar signals transmitted has been decreased to thenext lower power level, the received radar signals are analyzed forirregularities that are attributable to interference caused byneighboring radar transmitters, and if no irregularities are ascertainedin the received radar signals, the power of radar signals transmitted isincreased to a next higher stage.
 16. The method as recited in claim 12,further comprising: obtaining additional measured variables from a fieldof traffic surrounding the vehicle, the additional measured variablesincluding at least one of traffic noise and light radiated bysurrounding traffic, wherein the additional measured variables are usedto ascertain at least one of a traffic density and an interferencepotential dependent on the traffic density, for causing irregularitiesin the received radar signals reflected from target objects.
 17. Asystem for adaptively controlling the power of signals transmitted by aradar device having a radar transmitter for transmitting radar signalsand a radar receiver for receiving at the radar receiver radar signalsreflected from target objects, the radar device being mounted in avehicle, the system comprising: an analyzing unit for analyzing thereceived radar signals reflected from target objects for irregularities;and a control unit for reducing the power of radar signals transmittedby the radar transmitter if irregularities that are attributable tointerference caused by neighboring radar transmitters are detected inthe received radar signals reflected from target objects.
 18. The systemas recited in claim 17, wherein the analyzing unit includes aphase-locked loop circuit and a mixer for determining the frequency ofinterference signals.